Ocean waves that reach the shoreline of a land mass are primarily generated by wind pushing on the water surface far from land, but the energy contained in such waves is unpredictable, for a number of reasons. Unlike the predictable energy that can be extracted from water motion that is caused by tides, wave energy is subject to numerous modifying factors. For example, typically the wind will generate multiple waves which interact with each other in a random pattern, forming what is referred to as a fully developed sea. Accordingly, wave energy converters, unlike tide energy converters, must be able to adjust to different wave characteristics so that a maximum amount of energy can be extracted.
The surface of a single wave as it moves across the ocean bottom can be broadly described mathematically as equivalent to sinusoidal motion. However, it can be observed from the motion of the water surface that there are both vertical and horizontal vector components of velocity in a wave. The vertical component of velocity causes the wave to rise above and to fall below a mean waterline, while the horizontal component of wave velocity causes the wave crest to move in the direction of the wave propagation. It is less obvious that there is also a horizontal component of velocity opposite to the direction of wave propagation. These velocities can be depicted as four points along a wave in its direction of propagation, where the velocities are either horizontal or vertical. At the point of maximum wave amplitude, referred to as the wave peak, the velocity is horizontal in the direction of the wave propagation. Moving forward of the wave peak to the mean water line the velocity is vertically upward. At a point of minimum wave amplitude, referred to as the wave trough, the velocity is horizontal in the direction opposite to the wave propagation. Returning to the mean water line, the velocity is vertically downward.
The combination of these velocity vectors creates a circular velocity pattern, referred to as the orbital velocity. In deep water, the energy of a wave is split between the potential energy, which is the vertical motion in the direction of the rise and fall of the water surface, and the kinetic energy, which is the motion of the water parallel to the direction of wave propagation. The orbital velocities are strongest at the surface and decay down to zero at a depth of approximately one-half the wavelength, which is the distance between the peaks (or the valleys) of adjacent waves. In shallow water, where the water depth is less than one-half the wave length, the orbital velocities extend down to the ocean bottom. As the water depth becomes shallower than one-half of the wave length, the orbital velocity paths are compressed in the vertical direction, which flattens the paths into ovals.
The power in a single wave, per unit length of the wave (“Wave Power”, University of Strathclyde, 2001), can be expressed as:
      P    =                  ρ        *                  g          2                *                  a          2                *        T                    8        *        π                  Where    ⁢          :            P    =          power      ⁢                          ⁢              (                  kW          ⁢                      /                    ⁢          m                )                  ρ    =          the      ⁢                          ⁢      water      ⁢                          ⁢      density      ⁢                          ⁢              (                  kg          ⁢                      /                    ⁢                      m            3                          )                  g    =          acceleration      ⁢                          ⁢      of      ⁢                          ⁢      gravity      ⁢                          ⁢              (                  m          ⁢                      /                    ⁢                      sec            2                          )                  a    =          Wave      ⁢                          ⁢      amplitude      ⁢                          ⁢              (        m        )                  T    =          Wave      ⁢                          ⁢      period      ⁢                          ⁢              (        sec        )                  π    =          constant      =      3.14159      
From inspection of the equation above, it can be seen that the power of the wave corresponds to the wave amplitude squared. The wave amplitude is defined as the distance from the undisturbed mean water line to the top of the wave. The consequence of this relationship to a wave energy converter is that waves which are one-half the design wave amplitude will produce one-quarter the power. Similarly, wave amplitudes which are twice the design wave amplitude will result in four times the power. From this relationship it is recognized that the waves generated during a storm can easily overpower a wave energy converter designed for a typical wave height.
Numerous wave energy converters have been proposed and put into service. The devices strive to capture either the kinetic energy of a wave, the potential energy, or a combination of the two. Prior art wave energy converters can be divided into groups defined by how the wave energy is captured or absorbed. These groups are:                Attenuator—two floating devices connected by a pivot point that is parallel to the waves and bends due to passing waves.        Oscillating Water Column—a partially submerged chamber that focuses the wave energy when the wave enters the open end and forces air out of a smaller opening.        Oscillating Wave Surge Converter—a substantially vertical surface is mounted to an arm that is attached to a pivot on the sea bottom which moves back and forth due to passing waves.        Overtopping Device—a perimeter raised above the water surface allows waves to wash over the perimeter, thus raising the confined water level; energy is recovered when water is returned to the normal sea level.        Point Absorber—a float that rides up and down a vertical column due to passing waves.        Submerged Pressure Differential—the alternating pressures due to the rising and falling wave height are used to drive a mechanism.        Rotating Mass—the rising and falling waves are used to cause an eccentric weight to rotate about an axis.        
An example of the prior art in this field is found in U.S. Pat. No. 1,960,622 to DuPont, which describes a wave power plant having vertical panels suspended from a rod above the sea on hinge-like pivots so that passing waves apply force on each pivoting vertical panel to cause the panel to rotate about its pivot. The force applied to the panel is then supplied through rigid linkages to an electric generator. While the DuPont wave power plant does transfer wave kinetic energy from the wave through the mechanism to a generator, it requires a considerable amount of beach-front equipment and support structure.
Other examples of the prior art are found in U.S. Pat. Nos. 4,170,738 and 4,371,788 to Smith, which describe a similar vertical panel or sail device in which the panels move back and forth, guided by a pair of rails on the sea bottom. It should be noted that Smith's vertical panels remain vertical and, when moved, translate back and forth on the rails. U.S. Pat. No. 7,023,104 to Kobashikawa et al. describes a third variation on a prior art moving panel, in this case where the panel pivots about a point at the bottom. The Kobashikawa approach reduces the amount of support equipment that was required for the DuPont and the Smith systems, but the structural strength of the panel and the pivot foundation's integrity limited the power that could be produced from a single device. A more practical, economical and effective system for converting wave motion to electrical energy is needed, and is described herein.